This invention relates to methods and devices for recycling thermoplastic scrap and, more particularly, to methods and devices which permit the excess hot thermoplastic waste extruded out of the edges of phonograph records immediately after they are pressed in a hydraulic record press, to be cooled and reused as a constituent material in the production of new records.
The broad concept of cooling hot thermoplastic scrap so that it could be ground for reuse is well known. A method for melting and reusing thermoplastic scrap is disclosed by Corbett et al. in U.S. Pat. No. 3,607,999. The waste material falls on a conveyor, where it is heated and then densified by rollers. The hot scrap is then cooled by nozzles so that it can be ground in the grinder. From the grinder, the scrap is conveyed to a heated extruder for reuse.
Another method for recovering and utilizing thermoplastic scrap is disclosed by McKenzie, et al. in U.S. Pat. No. 3,883,624. The waste material is first ground, then heated and cooled so that it can be ground again in the grinder. The ground scrap is then blended with virgin resin in the blender and subsequently formed into a finished product.
These methods are complex, requiring many independent steps, using complicated, expensive and cumbersome machinery.
In the current conventional process of manufacturing plastic records, vinyl plastic powder from the grinder is dropped from a trough, into a vertical tube, where it is heated until it is liquified, then forced out of a small opening into a metal mold where it forms a "cake" about five (5) inches in diameter and one (1) inch thick. A slide cylinder places a label on top and bottom of the cake, and swings it into the hydraulic press, where upper and lower dies come together. The cake is squeezed by some 1800 psi of pressure, forming the record, and extruding a thin portion of the vinyl plastic around the edge of the record, called the "flash". Grippers on either side of the press grip or seize the record by the flash and carry it by sliding it across to two circular metal plates. The surfaces of the plates, which come in contact with the record, are made of rubber, which will not damage the record when the plates come together to hold the record in place.
The record and plates are rotated around a knife blade, which trims off the flash, allowing it to fall down in the shape of a vertical strip. This strip is received, at a temperature of approximately 200 degrees Fahrenheit, by a large barrel located beneath the apparatus. When the barrel is filled by the strips, it is pulled away manually, and brought to the grinder, where the strips, which have become intertwined forming a loose mass, are then ground, in bulk, to form new vinyl plastic powder, which is then reheated and forced into the extruder, and the system begins anew.
A disadvantage of the current system is that the barrels take up a lot of space, limiting the number of record press machines that can be operating in a given area. More machines would mean greater profits to the record manufacturer since the record output would be increased. However, manufacturing space is expensive and any increased profit that would flow from an increase in the number of machines, would be reduced by having to provide more space to contain them.
The strips of flash that are trimmed from the hot, newly formed records take a long time to cool, and must be transported manually to the grinder. This creates a further financial investment since the slow cooling process further delays the operation, and the manual labor needed to transport the material is expensive.
Feeding a large number of the intertwined strips into the grinder causes the blades to continually wear down and require replacing, again slowing the operation.
A further drawback is that the current system is not energy efficient, and requires use of independent electrical, hydraulic or other energy sources to operate.
In general, the prior art methods are complicated, in that they require numerous sophisticated, independent operations to function. They are discontinuous, thereby slowing down production time, and require expensive equipment and manpower to operate.